1. Field of the Invention
The present invention relates to fluid driven and fluid driving machines, compressors for example.
2. Description of the Prior Art
A previously proposed rotary piston compressor has a circular and rigid piston, of which the diameter may be up to approx. 10% smaller than the cylinder diameter. The piston is pressed against a cylinder wall by an eccentric crank drive. In order to produce a suction and pressure chamber, the cylinder carries a radially movable separating slide which is pressed against the rotary piston by spring pressure. During one rotation, there is an induction stroke and an expulsion stroke.
As long as the piston is pressed against the cylinder wall with sufficient initial tension, the piston will roll by virtue of its smaller diameter and in accordance with the equation: ##EQU1##
This means that for 10% smaller diameter, the piston rolls in opposition at 10% smaller diameter at i=(-) 10, in other words one-tenth of the rotary speed of the camshaft, but naturally only as long as the friction moment between cylinder and piston is greater than the bearing friction moment. Therefore, functionally what is involved is a single planet friction wheel transmission with a cam drive. Balancing is by means of counterweights on the crankshaft. There is linear contact at the rolling point and, for adequate pressure, the linear contact flattens out according to the Hertzian equation.
By reason of the reduced rolling speed of the piston, sealing between the separating slide and the piston presents no particular problems. The main problems, particularly when the unit is used as a compressor, arises at the point of contact between piston and cylinder.
Insufficient applied pressure interferes with the rolling process and, due to an increase in the rotary speed of the piston, leads to friction wear and sealing errors. Non-circularity means that the piston becomes incapable of functioning. Excessive applied pressure increases the Hertzian pressure. After a short period of operation, faults occur due to material fatigue. The rolling process becomes kinematically disturbed by the cylinder slot housing the separating slide. The width of the separating slide is greater than the flattening-out caused by the Hertzian pressure so that at this point the piston emerges from the frictional closure. The cross-section to accommodate the separating slide extends over the total width of the piston. The friction moment exerted by the separating slide is naturally smaller than the bearing friction moment. At this point, the piston emerges from its frictional closure. The forces occasioned by compression counteract the force of application.
The object of the invention is to avoid these drawbacks and to enhance the seal between the separating elements on the one hand the piston on the other hand and furthermore to ensure that the wear on the piston is reduced substantially to zero.